Studies were continued on the isolation, purification and characterization by chemical, biochemical and immunological procedures of biologically active polysaccharides from a number of pneumococcal types, Leuconostoc mesenteroides, Streptococcus, Plasmodium berghei, Plasmodium vinckei and certain plant materials. Further studies on the molecular structure of the serologically active polysaccharide from Carthemus tinctorius were also carried out. In addition, polysaccharides from flowers of 20 ornamental plants were isolated and tested for cross-reactivity with Type III pneumococcal rabbit and horse antisera. Of the 20 polysaccharides two - Geranium maculatum and Petunia hybrida vilm - reacted with high titers to rabbit and horse antisera to pneumococcus Type III in precipitin tests and lines of precipitation in the Ouchterlony tests were confluent with those of the pneumococcal Type III polysaccharide. In vivo experiments with the two most serologically active polysaccharides showed these materials to be highly immunogenic. Structural analyses of these materials have indicated that repeating units of specifically linked monsaccharides are extremely complex. BIBLIOGRAPHIC REFERENCES: Brunner, H., Prescott, B., James, W.D., Horswood, R.L., and Chanock, R.M.: Unexpectedly high frequency of antibody to Mycoplasma pneumoniae in human sera as measured by sensitive technique. J. Infect. Dis. 135: 524-530, 1977. Helms, C.M., Grizzard, M.B., Prescott, B., Senterfit, L., Urmacher, S., Schiffman, G., and Chanock, R.M.: Preparation and characterization in vitro of ts mutants of Type I S. pneumoniae. J. Infect. Dis. 135: 582-592, 1977.